1. Field of the Invention
The invention generally relates to the field of power saving technology, and more particularly, to save power by efficiently switching operation modes of mobile communication devices for paging operations.
2. Description of the Related Art
In a typical mobile communication environment, a service network may transmit a paging message via the paging channel to inform a mobile station that wireless services, including voice and/or data services, are about to take place. Generally, the paging channel may be further divided into a plurality of time slots for unambiguously paging different mobile stations, i.e., each mobile station is assigned with a time slot on the paging channel. As shown in FIG. 1, the mobile stations MS1˜MSn are assigned with the time slot Ts1, the mobile stations MSn+1˜MSy are assigned with the time slot Ts2, and so on. Particularly, the mapping relationships between the mobile stations and the time slots are in a predetermined cycle. According to the assignments, each mobile station has to monitor the assigned time slot for paging messages, and in order to save power, the mobile station may turn off the function of wireless transceiving and enter a standby mode (or so-called sleep mode) for the other time slots.
Taking the Code division multiple Access 2000 (CDMA 2000) system for example, a mobile station operating in the slotted mode is assigned with a specific time slot for monitoring the paging channel, wherein each time slot is 80 milliseconds (ms) long and comprises 4 frames. Before the assigned time slot, the mobile station may enter the standby mode to save power, and later, leave the standby mode to receive a complete frame when in the assigned time slot. Subsequently, the mobile station may decode the received frame to obtain a paging message. It is noted that, the reception of the frame involves module operations, such as turning on the receiving (Rx) Radio Frequency (RF), Rx RF Phase-Locked Loops (PLLs), Rx Analog to Digital Converter (ADC), and digital baseband for more than 20 ms. According to the received frame, the mobile station may determine whether it is necessary to continue to monitor the paging channel. If not, the mobile station may turn off the modules for the Rx operations and enter the standby mode. FIG. 2 is a timing chart illustrating a paging operation of a mobile station in the slotted mode. As shown in FIG. 2, a mobile station is assigned with the time slots Tsx and Tsx+n−1, i.e. the time slots on the paging channel are repeated at every n time slots. The mobile station wakes up (i.e., leaves the standby mode) before the assigned time slot, to turn on the modules for Rx operations, so that the Rx operations may be performed on time for the assigned time slot. To further clarify, in time slot Tsx−1, the mobile station first turns on the Rx RF PLLs, and turns on the Rx RF and Rx ADC when the Rx RF PLLs is settled. Next, the mobile station searches for finger allocation when the Automatic Gain Control (AGC) of the Rx ADC is settled, and allocates finger(s) receiver before the time slot Tsx for receiving a paging message in the time slot Tsx. After that, the mobile station demodulates the symbols received in the time slot Tsx, and later, when a first frame is received after 20 ms, the mobile station decodes the first frame, and the second, until the message included in this slot is correctly received or until the last frame of the slot. The mobile station may determine whether it has been paged in the time slot according to the decoding result. If not, it means that it is unnecessary for the mobile station to monitor the paging channel in this time slot, so the mobile station turns off the Rx RF, Rx RF PLLs, and Rx ADC in sequence, and then enters the standby mode until the time slot prior to the next assigned time slot.